The finer details I would leave to the various stakeholders and legislators. I don't have enough background to comment wisely.
But Dave Tomlinson advocated for a higher grade license for high grade firearms. It might be easy to get a license for a 22, but a pistol requires more criteria. Again, the finer details belong to someone other than me.
Unfortunately, the program needs to be national, not state-by-state. The states can set up their own requirements, which can be stricter or more leneint. But at the end of the day, if a user has no license, the firearm is confiscated. It shouldn't matter whether the rule is federal or state.
I'm sure the police will use a lot of good judgment for those who do not immediately comply. Warnings and time will be given to get properly licensed for many unlicensed firearm users. But if the user is a known gang member or someone who behaves erractically, take the gun away now.
And yes, an appeal process is necessary.